Antimicrobial Use and Stewardship

CDFA-AUS  •  1220 N Street, Sacramento, CA 95814  •  916-576-0300

Resources & Outreach

The AUS program provides resources for all stakeholders, including veterinarians and producers, about the effort in California to reduce antimicrobial resistance in livestock. Below please find outreach and educational materials, best management practices and guidance documents, programmatic reports, and other publications produced or supported by the AUS program. Information on AUS presentations and events, past and upcoming, is also provided. Additionally, other resources related to antimicrobial resistance education and research are listed.

Frequently Asked Questions: Answers to frequently asked questions regarding the AUS program.
English  |  Spanish (Español: Preguntas Frequentes)
Requirements for Prescription Antibiotics: Existing requirements for veterinary prescriptions, options for filling prescriptions, and establishing a valid veterinarian-client-patient relationship (VCPR).
Veterinarian   | Producer | Spanish (Español: Requisitos para Antibióticos Recetados)
AUS Annual Reports: Description and highlights of program activities reported for each fiscal year. Attached appendices provide more detailed information for a selection of AUS' studies and projects.
AUS 2021 Annual Report
AUS 2020 Annual Report
AUS 2019 Annual Report | News Release
Veterinary Feed Directive (VFD) Summary Reports: Annual summaries of manufacturing and distribution data for California medicated feed containing a VFD drug or combination VFD drugs, by VFD order written by a licensed veterinarian.
2019 Veterinary Feed Directive Summary Report
Summary Report Veterinary Feed Directive 2017 – 2019 Q1
AUS Report to the Legislature: The AUS Report to the Legislature, published in 2019, fulfills the mandate in FAC 14405 (d) by providing the results of the program’s outreach activities and monitoring efforts during its first years of implementation.
AUS Report to the Legislature | News Release
AUS Strategic Plans: AUS publishes its Strategic Plans as appropriate to update stakeholders on programmatic goals and plans for implementation.
2018 Strategic Plan
CAHFS Antibiogram Development Process: These slides outline the steps involved in creating Minimum Inhibitory Concentration (MIC) data and how the MIC data is used to develop antibiograms based on the process currently utilized by the California Animal Health and Food Safety Laboratory (CAHFS). California Livestock Antibiograms: A User Guide: This document serves as a guide for veterinarians on how to interpret and apply antibiograms in clinical practice. Antibiograms are a clinical tool that can help optimize veterinary approaches to antimicrobial therapy, specific to a particular bacteria and drug combination. Please note: All CAHFS antibiograms are for advisement only and are intended to be used by veterinarians.
CDFA AUS – Best Management Practices (BMPs) // Vaccine Handling Guidelines: Five infographics providing foundational knowledge of proper vaccine handling to ensure an effective vaccination program.

CDFA AUS – Best Management Practices (BMPs) // Vaccine Handling Guidelines – Resources for Veterinarians: These veterinary considerations offer a more in-depth instruction on the nuances of creating an effective vaccination program, along with additional scientific resources.

CDFA AUS – BMPs for Vaccine Handling Guidelines | Español: CDFA AUS - Buenas prácticas de manejo // Pautas de Manejo de Vacunas
CDFA AUS – BMPs for Vaccine Handling Guidelines - Resources for Veterinarians
Antimicrobial Stewardship Principles: Please visit the AUS Antimicrobial Stewardship page. Guidelines for Judicious Use of Antimicrobials: These guidelines are intended to support decision-making surrounding responsible antibiotic use, under the guidance of a veterinarian in compliance with state and federal laws.
Guidelines for Judicious Use of Antimicrobials in Livestock
Guidelines for Veterinarians: Judicious Use of Antimicrobials in Livestock
Responsible Antibiotic Use infographic
Antimicrobial Stewardship Planning Checklist: Resources to promote or support veterinarians engaging in conversations with their livestock producers regarding broad, non–species specific health related topics.
Antimicrobial Stewardship Planning Checklist One–Page | Español: Lista de verificación para la planificación de administración de antimicrobianos de una página
Antimicrobial Stewardship Planning Checklist Workbook | Español: Cuaderno de trabajo de la lista de verificación para la planificación de administración de antimicrobianos
Veterinarian–Client–Patient Relationship (VCPR) Resources: Establishing a veterinarian–client–patient relationship (VCPR) is an essential first step in the development of an Antimicrobial Stewardship Plan.
VCPR Practice Model – Youth Agriculture
VCPR Example – Agent Authorization
2017 Cow Calf Survey: Summary findings from AUS’ 2017 survey of antibiotic use and stewardship on California’s cow calf operations.
2017 Cow Calf Survey | Español: Encuesta de Terneros 2017
2018 Commercial Sheep Survey: Summary findings from AUS’ 2018 survey of antibiotic use and stewardship on California’s commercial sheep operations.
2018 Commercial Sheep Survey | Español: Encuesta de Ovejas Comerciales 2018
Partnering for Dairy Antimicrobial Stewardship: A Conference for Farmers and Veterinarians in the West (July 2020)
Recordings: July 8 | July 15 | July 22 | July 29
Upcoming: Visit here for information on upcoming AUS presentations, events, and opportunities to get involved with the program.
Distinguishing Between US and CA Antibiotic Laws: Easy-to-read flowchart explains medically important antimicrobial drugs (MIADs) and related laws.
English | Spanish (Español: ¿Cómo Distinguir entre las leyes sobre antibióticos de EE.UU. y California (CA)? Gráfico)
Veterinary Feed Directive (VFD) Resources: Resources related to VFDs and VFD orders. For more information on VFDs, please visit the CDFA FFLDRS Livestock Drug Program page.
CDFA Feed Program's VFD page
VFD Checklist
Common Issues on Veterinary Feed Directives
Filling a Veterinary Feed Order
Confidentiality in Data Reporting: Brochure with information on AUS’ approach to confidentiality in data reporting. AUS Surveys & Studies Resources: Materials addressing the who, what, why, and how the AUS program is collecting information on California animal agriculture and what you can do to help. For more information on AUS Surveys & Studies, please visit the Surveys & Studies page.
AUS Surveys & Studies Trifold
AUS Surveys & Studies Participation Flier
Antimicrobial Stewardship During COVID-19 Pandemic: COVID-19 has brought numerous challenges to the animal production industry. This infographic lists considerations for the continuation of antimicrobial stewardship in livestock during the COVID-19 pandemic.
In addition to materials, events, and research produced by the AUS team, the AUS program provides funding and support for a number of studies, projects, publications, and other resources led by external partners. Below find information on work produced with AUS funding and/or collaborative support.

Please Note: The New flag indicates publications new to this list, not necessarily chronological in time for work performed or publication date. To facilitate searching for subjects of interest, keywords have been provided for each publication.
New Abdelfattah EM, Ekong PS, Okello E, Chamchoy T, Karle BM, Black RA, Sheedy D, ElAshmawy WR, Williams DR, Califano D, Tovar LF. Epidemiology of antimicrobial resistance (AMR) on California dairies: descriptive and cluster analyses of AMR phenotype of fecal commensal bacteria isolated from adult cows. PeerJ. 2021;9. https://peerj.com/articles/11108/

This study describes the occurrence of antibiotic resistance in commensal Escherichia coli and Enterococcus/ Streptococcus spp. isolated from fecal samples of dairy cows and assesses the variation in antibiotic resistance profiles across regions and seasons following the implementation of the Food and Agricultural Code (FAC) Sections 14400 - 14408 (formerly known as Senate Bill, SB 27) in California.

Keywords: antimicrobial resistance; dairy cattle; Escherichia coli, Enterococcus spp; multidrug resistance, phenotype; California; region; season; cohort study
New Abdelfattah EM, Ekong PS, Okello E, Williams DR, Karle BM, Rowe JD, Marshall ES, Lehenbauer TW, Aly SS. 2019 Survey of Antimicrobial Drug Use and Stewardship Practices in Adult Cows on California Dairies: Post Senate Bill 27. Microorganisms. 2021 Jul;9(7):1507.507. https://doi.org/10.3390/microorganisms9071507

In this project, surveys were sent out to 1282 California dairies in both 2018 and 2019 to determine and evaluate changes in antibiotic use, health management, and antibiotic drug stewardship practices of adult cows on California dairies following the initiation of implementation of California Food and Agriculture Code 14400 - 14408 (formerly SB 27).

Keywords: antimicrobial drug resistance; antimicrobial stewardship; California; dairy cattle; judicious use; survey
Basbas C, Byrne BA, Chigerwe M, Escobar ED, Hodzic E, Pires AF, Pereira RV. Detection of Cephalosporin and Fluoroquinolone Resistance Genes via Novel Multiplex qPCR in Fecal Salmonella Isolates From Northern Californian Dairy Cattle, 2002 - 2016. Frontiers in Microbiology. 2021;12. https://doi.org/10.3389/fmicb.2021.601924

In this study, Salmonella isolates obtained from dairy cattle were screened for beta-lactam resistance genes, focusing on genes linked to resistance to cephalosporin drugs, and quinolone resistance genes. Testing included whole genome studies focusing on isolates resistant to quinolones to identify potential chromosomal mutations leading to resistance to quinolone drugs. Temporal distribution of genetic elements was evaluated for links to antibiotic resistance, as well as potential trends or factors that could have influenced changes in their prevalence.

Keywords: fluoroquinolone; cephalosporin; qPCR; antimicrobial resistance genes; Salmonella
New Depenbrock S, Aly S, Wenz J, Williams D, ElAshmawy W, Clothier K, Fritz H, McArthur G, Heller M, Chigerwe M. In-vitro antibiotic resistance phenotypes of respiratory and enteric bacterial isolates from weaned dairy heifers in California. PLoS One. 2021 Nov 24;16(11):e0260292. doi: 10.1371/journal.pone.0260292. PMID: 34818352; PMCID: PMC8612539. https://pubmed.ncbi.nlm.nih.gov/34818352/

This study provides information regarding antibiotic resistance in respiratory bacteria associated with bovine respiratory disease (BRD) and identifies relationships between respiratory and enteric antibiotic susceptibility. A cross-sectional study was performed between June 2019 and February 2020 on six calf rearing facilities in California. Antimicrobial resistance, including multidrug resistance, in respiratory isolates appears to be widespread in weaned dairy heifers. Enteric bacterial susceptibility appears to have limited direct association with respiratory isolate resistance classification.

Keywords: antimicrobial resistance; multidrug resistance; bovine; dairy; heifers; MIC; respiratory; Pastuerella multocida; Entrerococcus; Escherichia coli; tetracyclines; bacterial pathogens; cattle; penicillin; enteric; California
New Ekong PS, Abdelfattah EM, Okello E, Williams DR, Lehenbauer TW, Karle BM, Rowe JD, Aly SS. 2018 Survey of factors associated with antimicrobial drug use and stewardship practices in adult cows on conventional California dairies: immediate post-Senate Bill 27 impact. PeerJ. 2021 Jul 13;9:e11596. https://peerj.com/articles/11596/

This project examined good antibiotic drug stewardship practices on conventional dairies in California using survey data from 2018 that was previously described in another publication. The authors applied machine learning to model the associations between management practices and seven outcome variables relating to antibiotic use and stewardship.

Keywords: California dairy industry; antimicrobial drug use; antimicrobial stewardship; judicious use of antibiotics; risk factors; logistic regression; machine learning; decision tree; random forest; gradient boosting
New Ekong PS, Abdelfattah EM, Okello E, Williams DR, Lehenbauer TW, Karle BM, Rowe JD, Marshall ES, Aly SS. 2018 Survey of antimicrobial drug use and stewardship practices in adult cows on California dairies: post-Senate Bill 27. PeerJ. 2021 Jul 13;9:e11515. https://peerj.com/articles/11515.pdf

In this project, surveys were sent out to 1282 California dairies in both 2018 and 2019 to determine and evaluate changes in antibiotic use, health management, and antibiotic drug stewardship practices of adult cows on California dairies following the initiation of implementation of California Food and Agriculture Code 14400 - 14408 (formerly SB 27).

Keywords: California dairy industry survey; antimicrobial resistance; antimicrobial stewardship; antimicrobial drugs (AMD); judicious use of AMD
Hollister, Julia. “Dry Cow Therapy: A Prescription for Success.” Progressive Dairy, 26 Aug. 2020, www.progressivedairy.com/topics/herd-health/dry-cow-therapy-a-prescription-for-success.

An article published in the publication Progressive Dairy promoting an AUS funded study that explores the use of Selective Dry Cow Therapy in dairy herds and the opportunity to reduce the use of antibiotics in dairy production systems, which may also be an economic opportunity for dairy farmers.
New Hommels NM, Ferreira FC, van den Borne BH, Hogeveen HT. Antibiotic use and potential economic impact of implementing selective dry cow therapy in large U.S. dairies. Journal of Dairy Science. 2021 Apr 30. https://doi.org/10.3168/jds.2020-20016

In this study, the objectives were to evaluate the economic feasibility of implementing selective dry cow therapy (SDCT) in large U.S. dairy herds and to estimate the potential reduction in antibiotic use around the dry period if SDCT management is adopted. Cow-level data were obtained from the Dairy Herd Improvement Association and individual dairy herds in California. Logistic regression models were used to predict the incidence risk of subclinical and clinical mastitis in the subsequent lactation for 96 last test-day somatic cell score categories. This study showed that it is economically feasible on some farms to reduce antibiotic use associated with dry cow therapy in large U.S. dairy herds. This contributes to the efforts of reducing antibiotic use worldwide.

Keywords: selective dry cow therapy; antibiotic use; economics; optimization
Michael A, Kelman T, Pitesky M. Overview of quantitative methodologies to understand antimicrobial resistance via minimum inhibitory concentration. Animals. 2020 Aug;10(8):1405. https://doi.org/10.3390/ani10081405

Minimum Inhibitory Concentration (MIC) testing is a common method of measuring the susceptibility of bacteria to antibiotic drugs. Several quantitative techniques exist for analyzing MIC data, but the application of these methods is not consistent across studies and no guidelines exist for how to choose the most appropriate method. The purpose of this paper is to outline important considerations for selecting the appropriate analytic method to use with MIC data based on the purpose and context of the study.

Keywords: MIC; AMR; mixed effect models; logistic regression; cumulative logistic regression; accelerated failure time-frailty models; mixture models
New Okello E, Williams DR, ElAshmawy WR, Adams J, Pereira RV, Lehenbauer TW, Aly SS. Survey on antimicrobial drug use practices in California preweaned dairy calves. Frontiers in Veterinary Science. 2021;8. https://doi.org/10.3389/fvets.2021.636670

This survey allows immediate assessment of the impact of VFD final rule implementation and provides baseline data for future evaluation of the impact of VFD as well as SB 27 regulatory changes. The knowledge gained from this study is a valuable resource that could guide future recommendations for best health management practices and promote antibiotic stewardship efforts.

Keywords: antimicrobial drug use; veterinary feed directive; perception; preweaned dairy calves; California Senate Bill 27
New Sheedy DB, Okello E, Williams DR, Precht K, Cella E, Lehenbauer TW, Aly SS. Effect of Antimicrobial Treatment on the Dynamics of Ceftiofur Resistance in Enterobacteriaceae from Adult California Dairy Cows. Microorganisms. 2021 Apr;9(4):828. https://doi.org/10.3390/microorganisms9040828

This study investigates the time to peak population and time to return to pre-treatment population of phenotypically ceftiofur-resistant enteric commensal bacteria in response to systemic antibiotic treatment, in commercial dairy cows during the first 60 days of lactation, on two California dairies each across two seasons.

Keywords: antimicrobial resistance; ceftiofur; medically important antimicrobial drugs; dairy; minimum inhibitory concentration
New Sheedy DB, Samah FE, Garzon A, Fausak E, Van Noord M, Angelos JA, Maier GU. Non-antimicrobial approaches for the prevention or treatment of infectious bovine keratoconjunctivitis in cattle applicable to cow-calf operations: A scoping review. Animal. 2021 Jun 1;15(6):100245. https://www.sciencedirect.com/science/article/pii/S1751731121000872

Findings of the AUS 2017 Cow Calf Survey of California producers showed that pinkeye was one of the top three diseases of concern in this livestock population. In response, AUS funded a study to further explore options for producers to reduce the burden of this disease. In this scoping review, various non-antibiotic options for management of pinkeye were explored, resulting in the determination that further research is needed on the efficacy of fly control, and on non-antibiotic treatment options such as topical disinfectants or immune stimulants. The continued search for a viable vaccine, as well as identifying genetic markers associated with traits that confer resistance to the disease, are also needed.

Keywords: breed susceptibility; fly control; Moraxella bovis; pinkeye; vaccine